Multiple-capacitance condensers are utilized for interference abatement, e.g. as power line filters, electromagnetic interference suppression devices and, in general, to eliminate radio-frequency interference. As described, in U.S. Pat. No. 5,179,362, for example, X-capacitors and Y-capacitors may be provided as line filters in which, for example, two Y-capacitors are provided, one of which is connected between the phase or a load line and the protective line or ground while the other Y-capacitance is connected between the neutral line and the protective line or ground. The X-capacitance is connected between the phase or load line and the neutral line. All three capacitances can be incorporated in an X-Y-condenser or capacitor so that in a single unit a multiplicity of capacitances are provided which can be connected in various ways. Such multiple capacitance systems are provided in a variety of configurations.
For example, EP-B-0 090 170 describes a capacitive filter with one winding which is composed of at least a first strip of dielectric material which has at least one continuous metal coating leaving the sides of the strips uncovered and at least a second strip of a dielectric material having two continuous metal coatings which extend to the lateral edges of the strip and are separated by a zone free from a metal coating. The tapping of the various capacitances from this unit utilizes at least one cut out in the coil which extends from an end of the coil substantially to the separating zone between the metal coatings of the second strip.
To form a condenser with at least one X-capacitance and two Y-capacitances, two cut outs in the condenser coil are necessary. These cut outs can be obtained by a milling operation and to ensure optimal self-healing characteristics of the mechanically-divided condenser coil segments, these cuts generally should be inclined to the axis. This method of fabricating a condenser with multiple capacitances has been found to be very expensive and disadvantageous because it requires, in addition to the machines which are usually provided for winding of the condenser and packaging of the wound condenser, at least one high-precision milling machine and the equipment and space necessary for transporting the condenser body between machines, for delivering the condenser blank to carrying the milled condenser blank away from the milling machine, etc.
The high cost of such a system has been recognized heretofore and in EP-B-0 190 090, a process has been proposed for producing a condenser with a winding which allows the fabrication of multiple capacitances, utilizing a demetalized zone at least in one of the metal layers and usually in each of the windings. These demetalized zones should be oriented substantially radially in the turns of the winding. For the production of an X-Y-condenser, three such demetalized zones are necessary, preferably in a star-shaped arrangement. The demetalization must be provided for each layer of the winding and thus during each turn thrice in the case in which the demetalized zones subdivide the winding into three segmental capacitances. An electrode must be vapor-deposited at appropriate locations of the metalization on the foil. The process of fabricating the multiple- capacitance condenser is greatly slowed by the added steps required and, indeed, this method of fabricating multiple-capacitance condensers has been found to be largely uneconomical. In fact, even though milling machines are not required, the process has been found to be far too expensive to be used for economical mass production of multiple-capacitance condensers.
EP-B-0 222 547 describes a further condenser with multiple capacitances which can be wound from a greater number of dielectric and electrically-conducting strips and which requires that conductor strips be wound into the coil during the winding process to allow the capacitances to be tapped from the condenser. Ultrasonic welding or similar techniques are used to bond the connecting strips with the foils to which connection must be made. This construction has also been found to be excessively expensive and cannot be utilized effectively with paper-metal-foil condensers, with metalized plastic foil condensers, with metalized paper condensers, i.e. the types of condensers with which the invention is primarily concerned.
Finally, mention may be made of EP-P-0 215 361 which describes a wound condenser with multiple capacitances in which the individual capacitances are separated from one another by cuts into the winding. This system and the problems thereof are similar to those which obtain with EP-B-0 190 090.